Postemergent herbicide compositions containing acetoxy-terminated silicone glycol and dispersant

ABSTRACT

There is disclosed a herbicide composition in which a postemergent herbicide is activated by the inclusion of a silicone glycol adjuvant consisting essentially of (i) a silicone glycol having an average structure ##STR1## wherein Me denotes a methyl radical, and (ii) a silicone glycol dispersant compound for component (i). When compared to similar prior art silicone glycol adjuvants not having an acetoxy terminated glycol chain, the compositions of the present invention provide enhanced rainfastness in the control of weeds, particularly velvetleaf plants.

This is a divisional of application Ser. No. 07/439,906, filed Nov. 21,1989, now U.S. Pat. No. 4,933,002 issued Jun. 12, 1990.

This invention relates to postemergent herbicide formulations. Moreparticularly, the present disclosure relates to a composition of apostemergent herbicide which is activated by the inclusion of aparticular silicone glycol adjuvant consisting essentially of (i) asilicone glycol having an average of seven ethylene oxide units in itsglycol chain, said glycol chain being terminated by an acetoxy group,and (ii) a silicone glycol dispersant compound.

BACKGROUND OF THE INVENTION

It is well recognized in the art that the full potency of a givenorganic herbicide is not generally attained without the inclusion ofvarious adjuvants, an adjuvant being broadly defined as any substancewhich enhances the effectiveness of the herbicide. Thus, for example,through proper formulation with an activity-increasing adjuvant, thedamage inflicted upon a particular plant species by an herbicide can beamplified many fold. Such an activity-increasing adjuvant does notgenerally have biological activity on its own but only brings out theactivity of the herbicide.

An example of the aforementioned activity-increasing adjuvants is theclass of surfactants known as silicone glycols. These liquids have beenshown to enhance the efficacy of various herbicides. L. L. Jansen (WeedScience, v. 21, pages 130-135, March, 1973) examined the effect ofadding various silicone glycol adjuvants to different herbicides andfound that these adjuvants were superior to a standard organicsurfactant in eight plant species. In this study, cationic aminosilicone surfactants were also evaluated, but found to be less effectivethan the organic material. In any event, no specific structures of thesilicone compounds were provided in this paper.

Great Britain Patent Number 1,255,249 to Dow Corning Corporation againdiscloses herbicide compositions employing silicone glycol copolymers.Here, general utility of a large number of adjuvants is professed, asexemplified by two generic silicone glycol formulas which embracestructures having both diorganosiloxane units and alkyl-glycol siloxaneunits. There is also provided a wide-ranging list of suitableherbicides. This reference, however, provides little direction to thoseskilled in the art as to which particular silicone glycol structures areto be advantageously combined with specific herbicides, save for twoexamples employing a triazine herbicide in conjunction with an adjuvanthaving 1.8 siloxy units and bearing a glycol chain having 12 ethyleneoxide units.

In addition to the herbicidal enhancement provided by theactivity-increasing adjuvants discussed above, it is often importantthat herbicide formulations retain a significant degree of activity whenplants treated therewith are exposed to rain shortly after application,this being a definition of the degree of "rainfastness." This isparticularly critical in the case of water-soluble postemergentherbicides, such as acifluorfen-sodium, which are easily washed away byrainfall occurring within about six hours of application. Typically,this problem is currently addressed by inclusion of another class oradjuvants in the herbicide formulation, namely "sticking agents." Themain function of these materials, as the appellation implies, is toimpart an increased measured of adhesion of the herbicide composition toplant foliage and thus prevent premature washing away shouldprecipitation occur after the plants are sprayed. The sticking agentsare usually polymeric compounds which are generally water-insoluble andtacky in nature.

Neither of the above references addresses the issue of rainfastness nordo these references suggest to those of ordinary skill in the art howparticular silicone glycol compounds may be employed to provide bothenhanced herbicidal activity to particular herbicides as well asincreased rainfastness in the very same formulation, without resortingto the use of additional sticking agents.

In a copending application, Ser. No. 07/274,067, filed on Nov. 21, 1988,assigned to the assignee of the present invention and herebyincorporated by reference, it was shown that the rainfastness of apostemergent herbicide can be synergistically increased by the inclusionof a combination of a silicone glycol, and a dispersant for the siliconeglycol, in the herbicide composition. Quite surprisingly, theimprovement in rainfastness resulted only when the silicone glycol hadan average of four or five ethylene oxide units in its glycol chain.Neither this silicone glycol nor the dispersants therefor, providedrainfastness when used as the sole adjuvant in conjunction with theherbicide.

SUMMARY OF THE INVENTION

It has now further been found that a particular silicone glycol, notspecifically disclosed in the art, imparts an unexpectedly high degreeof rainfastness to post emergent herbicides. The present inventiontherefore relates to a composition consisting essentially of:

(I) a postemergent herbicide; and

(II) from about 0.01 to 50 parts by weight, for each part by weight ofsaid herbicide (I), of a silicone glycol adjuvant consisting essentiallyof

(i) from 20 to 95 weight percent of a silicone glycol having the averagestructure ##STR2## wherein Me denotes a methyl radical, and (ii) from 80to 5 weight percent of a silicone glycol dispersant having the averageformula ##STR3## wherein Me has its above defined meaning, R is adivalent alkylene group having 2 to 6 carbon atoms, Z is selected fromthe group consisting of hydrogen, an alkyl radical having 1 to 3 carbonatoms and an acyl group having 2 to 4 carbon atoms, n is 8 to 24 and xis 1 to 5.

The present invention further relates to a method for inhibiting thegrowth of weeds, particularly velvetleaf plants, comprising contactingat least part of the weed with a herbicidal formulation, the improvementcomprising using as said herbicidal formulation a homogeneous aqueousdispersion of the aformentioned composition.

DETAILED DESCRIPTION OF THE INVENTION

The herbicidal composition of the present invention is a homogeneousmixture consisting essentially of (I) a postemergent herbicide, (II) asilicone glycol adjuvant consisting essentially of (i) anacetoxy-terminated silicone glycol having seven ethylene oxide units inits glycol chain and (ii) a silicone glycol dispersant for siliconeglycol (i).

The postemergent herbicide (I) of the present invention is selected fromthose herbicides well known in the art to be effective when appliedafter the emergence of a plant. Examples of such postemergent herbicidesinclude, inter alia, 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one2,2-dioxide (bentazon) and N-(phosphonomethyl)glycine (glyphosate). Theformer herbicide is marketed under the trade name BASAGRAN by BASFWyandotte Corp., Parsippany, N.J. and the latter herbicide is sold underthe trade name ROUNDUP by Monsanto Agricultural Products Co., St. Louis,Mo.

For the purposes of the present invention, the herbicide is preferablyselected from the diphenyl ether structures exemplified by the generalformula ##STR4## Specific examples of this class of herbicides includesuch compounds as 2,4-dichlorophenyl 4-nitrophenyl ether (nitrofen);5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrobenzoic acid(acifluorofen); ethoxycarbonylmethyl2-[3-(2,6-dichloro-4-trifluoromethyl-phenoxy)-6-nitrophenoxy]-propionate;ethoxymethyl2-[3-(chloro-4-trifluoromethyl-phenoxy)-6-nitrophenoxy]-propionate;sodium 5-[2-chloro-4-(trifuoromethyl)phenoxy]-2-nitrobenzoate(acifluorfen-sodium); methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate(bifenox); and 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen). For the purposes of the present invention,acifluorfen-sodium is a preferred herbicide.

The silicone glycol (i) of the present invention has the averagestructure ##STR5## wherein Me hereinafter denotes a methyl radical. Thesilicone glycol (i) may be prepared by coupling the correspondingallyl-terminated glycol to a bis-siloxane structure having a hydrogenattached to the central silicon atom, said structure being ##STR6##Generally, the coupling is accomplished in the presence of a platinumcatalyst. The skilled artisan will recognize that, in such couplingreactions, a fraction of the allyl-terminated glycol is not convertedand will remain as an impurity in the final silicone glycol product.Additionally, as a result of inefficient distillation, theallyl-terminated glycol employed may contain a minor proportion ofmolecules having less than 7, or more than 7, ethylene oxide units.This, in turn, results in silicone glycols having less than 7 or greaterthan 7 ethylene oxide units, respectively. The herbicide compositionsmay contain such impurities and still be within the scope of the presentinvention.

The silicone glycol dispersant (ii) of the present invention is similarto the above described silicone glycol (i) and has the average formula##STR7## wherein R is a divalent alkylene group having 2 to 6 carbonatoms, Z is selected from the group consisting of hydrogen, an alkylradical having 1 to 3 carbon atoms and an acyl group having 2 to 4carbon atoms, n is 8 to 24 and x is 1 to 5. It is preferred that x is 1and n is about 12.

A highly preferred silicone glycol dispersant of the present inventionhas the average structure ##STR8##

In addition to the aforementioned components, the compositions of thepresent invention may also contain other herbicide adjuvants commonlyemployed in the art. Examples of such adjuvants include crop oilconcentrate, ORTHO X-77 spreader, drift control agents, such asLO-DRIFT, defoaming agents, such as D-FOAMER, other compatibilityagents, such as E-Z MIX, and other adjuvants well known in the herbicideart.

In order to prepare the compositions of the present invention, fromabout 20 to 95 weight percent of silicone glycol (i) is first thoroughlymixed with from about 80 to 5 weight percent of the silicone glycoldispersant (ii) to form the silicone glycol adjuvant (II). The optimumratio of these ingredients dependent upon the particular silicone glycoldispersant employed and is readily determined through routineexperimentation by the skilled artisan.

The above mentioned silicone glycol adjuvant (II) is then preferablyblended with herbicide (I) to form a homogeneous dispersion which canthen be diluted with water and sprayed onto plants according to themethod of the present invention, described infra. Alternatively, thesilicone glycol adjuvant (II) may be added directly to a water solutionor dispersion of herbicide (I).

In order to be within the scope of the present invention, from about0.01 to 50 parts by weight of the silicone glycol adjuvant (II) are usedfor each part by weight of herbicide (I). Preferably, from about 0.2 to17 parts by weight of the silicone glycol adjuvant (II) are so employed.

Preferred embodiments of the present invention employ silicone glycol(i) and the highly preferred silicone glycol dispersant, describedabove, in a weight ratio of about 2:1 to 9:1, respectively. In aparticularly preferred embodiment, this ratio is 4:1 and about 5 partsby weight of silicone glycol adjuvant (II) is used for each part byweight of herbicide (I).

In another aspect, the compositions of the present invention consistessentially of from about 0.02 to 2.0 parts by weight of postemergentherbicide (I), from about 0.01 to 50 parts by weight, for each part byweight of said herbicide (I), of the silicone glycol adjuvant (II) andsufficient water to provide 100 parts by weight of the totalcomposition.

The present invention also relates to a method for inhibiting the growthof weeds, particularly the species Abutilon theophrasti, hereinafterreferred to by its common name of "velvetleaf." This method comprisescontacting at least part of the weed with a homogeneous water dispersionof a herbicidal composition, as hereinabove described. This waterdispersion is applied to the foliage of the weed by any of the methodscommonly practiced in the art, preferably by spraying. The amount of thedispersion, and the herbicide contained therein, to be applied to thevelvetleaf may be varied to a great extent, the optima being determinedby such factors as soil conditions, weather conditions and the type ofcrops or other plants growing alongside the weed. Generally, however,the effective range is about 0.12 to 2 pounds per acre of herbicideformulation.

When the compositions of the present invention are used according to theabove described method, there is observed a marked improvement in therainfastness of the herbicide compositions relative to those containingsilicone glycol adjuvants having (on average) seven ethylene oxide unitsin the glycol chain wherein said glycol chain is not terminated with anacetoxy group. Thus, when compared with currently used silicone glycoladjuvants, there is provided a distinct advantage by the instantcompositions in that they permit the use of lower herbicide levels toattain a similar degree of injury to a weed when there is a reasonablelikelihood of precipitation after broadcasting the herbicide. Such areduction in herbicide levels generally results in reduced insult toadjacent cash crops and is considered highly desirable.

EXAMPLES

The following examples are presented to further illustrate thecompositions of this invention, but are not to be construed as limitingthe invention, which is delineated in the appended claims. All parts andpercentages in the examples are on a weight basis unless indicated tothe contrary.

Silicone glycols, having the average structure ##STR9## wherein Mehereinafter denotes a methyl radical and Q is defined in Table 1, wereprepared by the platinum catalyzed addition of the appropriateallyl-terminated glycol to an organohydrogenpolysiloxane having thestructure ##STR10## In Table 1, SILICONE GLYCOLE C is a commercialsilicone glycol, SILWET L-77 (Union Carbide Corp., Danbury, Conn.), andis believed to have the above structure wherein the glycol chain isterminated by a methoxy group.

                  TABLE 1                                                         ______________________________________                                        Silicone Glycol                                                                         Terminal Group Q                                                    ______________________________________                                        SILICONE  --OC(O)Me         (Acetoxy)                                         GLYCOL A                                                                      SILICONE  --OH              (Hydroxyl)                                        GLYCOL B                                                                      SILICONE  --OMe             (Methoxy)                                         GLYCOL C*                                                                     SILICONE  --OC(O)CH.sub.2 Me                                                                              (Propionate)                                      GLYCOL D                                                                      SILICONE  --OC(O)CH.sub.2 CH.sub.2 COOH                                                                   (Succinate)                                       GLYCOL E                                                                      ______________________________________                                         *SILWET L77 (Union Carbide Corp., Danbury, CT)                           

A silicone glycol having the average structure ##STR11## was employed asthe dispersant for the above described silicone glycols, and will bereferred to as DISPERSANT 1 herein.

The herbicide used in the examples was acifluorfen-sodium marketed byBASF Corporation (Research Triangle Park, N.C.) under the trade nameBLAZER.

EXAMPLES 1-10

Water dispersions of herbicidal compositions were prepared by firstthoroughly mixing the amount of SILICONE GLYCOL A through SILICONEGLYCOL C indicated in Table 2 with the amount of DISPERSANT 1. Thesemixtures were then blended with BLAZER (0.18 gm each) and each blend wasdiluted with water to provide 250 ml of total dispersion.

TEST PROTOCOL

Individually potted velvetleaf plants were grown under standardgreenhouse conditions in BACCTO professional potting soil mix.Temperature was controlled at 75+/-2° F. Irradiation consisted of normalsunlight supplemented by high-pressure sodium vapor lamps to provide anadded 1,200 μE/m². s at bench level (μE =microeinstein), wherein theday/night cycle was set at 18 hours and 6 hours, respectively.

When the plants were 3 to 5 inches tall, they were sprayed with waterdispersions of the herbicide compositions so as to broadcast herbicide(i.e., BLAZER) at a rate of 0.03 pounds per acre (0.03 lb/A) along withthe adjuvant (i.e., silicone glycol plus dispersant, when used). Theadjuvant rate was 3/4 pint/A when 0.94 grams of total adjuvant was used.Spraying was accomplished by means of a link-belt sprayer fitted with aTEEJET 8001 E nozzle which delivered the equivalent of 25 gallons/acreof the herbicide dispersion. In the spray apparatus employed, the 250 mlsamples, described above, provided the prescribed broadcast rates.

In addition, the rainfastness of the herbicide compositions wasevaluated by spraying half the plants with water in order to simulaterainfall. This procedure consisted of spraying plants from above (8-10inches above plant tops) using a TEEJET nozzle which delivered 0.4gallons of water per minute. This nozzle was also mounted on a chaindrive and reciprocally moved over four plants at a time, each suchtraverse taking about 9-10 seconds. The water spray was started 15minutes after application of the herbicide compositions and wascontinued for approximately 7 minutes, at which point the equivalent ofone inch of "rain" had fallen on each plant.

Plant injury was visually determined using a double-blind experimentalmode wherein four replicates were run for each herbicide composition.Phytotoxicity was ranked from zero, corresponding to no observableeffect, to 100%, corresponding to total destruction of the plant. Theseresults were averaged and the values reported using Duncan's multiplerange test to distinguish statistical differences at the 95% confidencelevel. As is common practice in the art, the injury values reportedinfra include lower case superscript letters which indicate whether anygiven set of values is statistically identical. Thus, for example, whentwo injury values have such a superscript in common, this is anindication that these values are not statistically different at the 5%level by Duncan's method.

The above described herbicide dispersions were used to spray velvetleafplants and the degree of injury, both with and without rain simulation,was observed seven days after spraying with the herbicide dispersions ofExamples 1-3. These results, along with the Duncan statisticalannotations, are presented in Table 2. As a control, four velvetleafplants were observed which were not sprayed with any herbicidecomposition.

                  TABLE 2                                                         ______________________________________                                        SILICONE       DISPER-                                                        GLYCOL         SANT 1     Percent                                                           Amount   Amount   Injury to Plant                               Example                                                                              Type   (gm)     (gm)     No Rain                                                                              With Rain                              ______________________________________                                        1      A      0.752    0.188    74.sup.d,e                                                                           71.sup.e,f                             2      A      1.25     --       60.sup.g                                                                             41.sup.j,k                             3      --     --       0.94     40.sup.j,k                                                                            5.sup.r,s                             4      --     --       0.752    38.sup.j,k,l                                                                          5.sup.r,s                             5      --     --       0.188    15.sup.p,q                                                                            0.sup.s                               6      B      0.752    0.188    83.sup.a,b,c                                                                         33.sup.l,m                             7      C      0.752    0.188    88.sup.a                                                                             43.sup.i,j,k                           8      C      0.94     --       80.sup.b,c,d                                                                         44.sup.h,i,j                           9      C      0.752    --       81.sup.a,b,c                                                                         36.sup.k,l,m                           10     --     --       (BLAZER   0.sup.s                                                                              0.sup.s                                                      alone)                                                 Control-(No BLAZER, No adjuvants)                                                                    0.sup.s  0.sup.s                                       ______________________________________                                    

It is apparent from Table 2 that the herbicide formulation containingthe silicone glycol having acetoxy-terminated glycol chains, incombination with DISPERSANT 1, provided significantly improvedphytotoxicity after exposure to simulated rain conditions relative tothe corresponding hydroxyl- and methoxy-terminated compounds.Furthermore, it is seen that DISPERSANT 1, SILICONE GLYCOL B andSILICONE GLYCOL C did not provide the improved rainfastness as did thecombination of DISPERSANT 1 and SILICONE GLYCOL A when a total of 0.94grams of each adjuvant was employed in the herbicidal composition.SILICONE GLYCOL A was less effective than the combination even whenemployed at a higher concentration (i.e., 1.25 gm).

EXAMPLES 11-16

Herbicidal composition were prepared and tested according to theprocedures of Examples 1-10 wherein only 0.94 grams of the siliconeglycols shown in Table 3 were mixed with 0.14 ml (0.18 gm) of BLAZER(i.e., no DISPERSANT 1 was added). As before, the herbicidalcompositions were applied to velvetleaf at a rate of 0.03 lb/A of BLAZERand 3/4 pint/A of the silicone glycol adjuvant. Table 3 indicates thatessentially no improvement in rainfastness is obtained by varying theglycol chain terminal groups when the dispersant was omitted.

                  TABLE 3                                                         ______________________________________                                        SILICONE GLYCOL     Percent Injury to Plant                                   Example                                                                              Type      End Group  No Rain With Rain                                 ______________________________________                                        11     A         Acetoxy    74.sup.a                                                                              30.sup.f,g                                12     B         Hydroxyl   73.sup.a                                                                              28.sup.f,g,h                              13     C         Methoxy    63.sup.b,c                                                                            33.sup.e,f,g                              14     D         Propionate 70.sup.a,b                                                                            35.sup.e,f                                15     E         Succinate  18.sup.h,i,j                                                                           0.sup.k                                  16          (BLAZER alone)   0.sup.k                                                                               0.sup.k                                  Control-(No BLAZER,  0.sup.k   0.sup.k                                        No adjuvants)                                                                 ______________________________________                                    

We claim:
 1. A silicone glycol having the structure ##STR12## wherein Medenotes a methyl radical.